Surely it's a difficult to compare a 2 stroke to a diesel regardless of age.

The NSR has a bang every stroke of the piston so it will look good on paper giving ~70bhp from a tuned 300 against 105bhp from a 600 (though a similarly tuned 600 is a lot more than 105bhp). Also remember the emmisions on your 300cc NSR probably exceed that of small country, whereas the R6 is working on less than a flatulent mouse .

Also it has to be said that the R6 (like any modern diesel) will rev like feck till you get bored, unlike an NSR unfortunately (though I do not speak from first hand experience...yet...touch wood).